1. Field of the Invention
The present invention relates to a photosensitive printing plate and a method of producing the same and, more particularly, to a photosensitive printing plate which is superior in vacuum contact properties and is free from tack on the surface when used, and is also superior in storage stability, and a method of producing the same.
This application is based on Japanese Patent Application No. 11-317405, the contents of which are incorporated herein by reference in their entirety.
2. Background Information
There has previously been employed a method of making a photosensitive printing plate and an original film which come closely into contact with each other under vacuum to make the original film and the surface of the photosensitive printing plate come closely into contact with each other, completely, when the photosensitive printing plate is exposed to light through the original film. In this method, since the smooth surface of the photosensitive printing plate prevents the space between the photosensitive printing plate and the original film from being evacuated, the time required to make the original film and the whole surface of the photosensitive printing plate come closely into contact with each other is lengthened, thereby drastically lowering efficiency of the plate making operation.
To reduce the time required for the original film and printing plate surface come closely into contact with each other while evacuating (hereinafter referred to as xe2x80x9cvacuum close contact timexe2x80x9d), Japanese Patent Application, First Publication No. 51-111102 has suggested a photosensitive printing plate produced by coating the surface of a photosensitive layer with a matting agent to form a fine pattern (mat particles) in which a coated portion and a non-coated portion are simultaneously present, while Japanese Patent Application, First Publication No. 55-12974 has suggested a photosensitive printing plate produced by thermally fusing solid powders to the surface of a photosensitive layer to form mat particles. However, materials of the mat particles in these photosensitive printing plates had drawbacks in that the mat particles are fractured by various pressures applied during the production, storage and use thereof because of poor mechanical strength, thereby lengthening the vacuum close contact time.
Japanese Patent Application, First Publication No. 57-34558 has suggested a photosensitive printing plate produced by spraying an aqueous solution, which is prepared by dissolving or dispersing a carboxyl group-containing water-soluble resin, over the surface of a photosensitive layer to form mat particles on the surface of the photosensitive layer. The mat particles of this photosensitive printing plate are superior in terms of adhesion to the photosensitive layer and have minimal peeling from the surface of the photosensitive layer by friction or pressure. In this photosensitive printing plate, a water-soluble resin is used as mat particles in view of the safety during the production thereof. However, since used water-soluble resin exhibits stickiness (tackiness) under the conditions of high temperature and high humidity, the mat particles on the photosensitive layer are adhered to the back surface of a substrate of the photosensitive printing plate, which is in contact with the mat particles, thereby making it impossible to transport using an automatic plate making machine, when pressure is applied on the surface of the photosensitive layer for a long period of time under conditions in which the photosensitive printing plates are stacked without interleaving paper between them.
Japanese Patent Application, First Publication No. 57-58152 has suggested, as a photosensitive printing plate having improved tack on the surface, a photosensitive printing plate produced by using a water-soluble resin containing an ammonium salt of acrylic acid unit as the resin for mat particles. However, when using such a resin, a photosensitive material in the photosensitive layer is decomposed after a lapse of time, thereby making it impossible to partially develop the photosensitive layer, resulting in poor storage stability.
Japanese Patent Application, First Publication No. 58-182636 has suggested a photosensitive printing plate produced by using a water-soluble resin having a sulfonic group as the resin for mat particles. However, when using such a resin, tack and storage stability under the conditions of high temperature and high humidity are improved but are still poor. That is, there were drawbacks in that a large content of the sulfonic group causes tack, while a large content of an alkali salt, an ammonium salt and a water-soluble amine salt causes poor storage stability.
An object of the present invention is to provide a photosensitive printing plate which has excellent vacuum contact properties and resistance to friction and pressure and is free from tack on the surface when used, and which causes no problem in developing properties during the storage for a long period of time.
The inventors have intensively studied to attain the above object and found that the above object can be attained by using, as mat particles, a copolymer containing (meth)acrylamides as a unit. Thus, the present invention has been achieved.
The photosensitive printing plate of the present invention comprises a substrate, a photosensitive layer formed on the substrate, and mat particles formed on the photosensitive layer, wherein the mat particles contain a copolymer which contains at least one (meth)acrylamides as a unit.
The method of producing the photosensitive printing plate of the present invention is a method of producing a photosensitive printing plate comprising a substrate, a photosensitive layer formed on the substrate, and mat particles formed on the photosensitive layer, the method comprising dissolving a copolymer containing at least one (meth)acrylamide as a unit in a solvent to prepare a solution, and coating the photosensitive layer with the solution to form mat particles.
The photosensitive printing plate of the present invention has excellent vacuum contact properties and resistance to friction and pressure and is free from tack on the surface when used, causes no problem in developing properties during storage for a long period of time, and is superior in terms of solubility in an exhausted developer. Regarding such a photosensitive printing plate, mat particles on the photosensitive layer are not adhered to the back surface of a substrate of the photosensitive printing plate, which is in contact with the mat particles, when a pressure is applied on the surface of the photosensitive layer for a long period of time in the state where the photosensitive printing plates are stacked without interleaving paper between them. Therefore the photosensitive printing plate of the present invention is preferably used in an automatic plate making machine.
According to the method of producing the photosensitive printing plate of the present invention, there can be produced a photosensitive printing plate which has excellent vacuum contact properties and resistance to friction and pressure and is free from tack on the surface when used, and also causes no problem in developing properties during the storage for a long period of time and is superior in solubility in an exhausted developer.